343 The Oligocene of the Southern United States 33 



Oligocene of the Gironde valley. The Oligocene of the 

 Gironde vallej^ is strongly developed on the right (northeastern) 

 side of the Garonne. Thus the large areas between the Garonne 

 and the Dordogne rivers, and between the Garonne and the Lot, 

 are made up almost entirely of deposits of this epoch. In addi- 

 tion, there are smaller areas, tvi'o north of the Dordogne in the 

 vicinity of Fronsac and St. Erailion, and one at Bourg, near the 

 junAion of the Garonne and the Dordogne. 



On the left (southwestern) side of the Garonne there are no 

 large areas, but exposures of this formation occur along the val- 

 leys of the many small tributaries of the river. Of these outcrops, 

 the most famous are those near Martillac. Saucats. La Brede and 

 Bazas. 



On the left side of the Gironde, where it widens, forming the 

 gulf, there are several outcrops as at Lesparre and Pauillac. 



A valuable discussion of the Oligocene of the Gironde valley 

 was published in 1895 by M. Fallot* of the University of Bor- 

 deaux. M. Fallot's contribution, which has done much in eluci- 

 dating the stratigraphy and paleontology of the region, has been 

 used as the basis of the following summary: 



Se^ion of the Gironde Oligocene. The Oligocene of the 

 Gironde vallley may be regarded as typical near Brazas. The 

 beds are greatly modified near Bordeaux. 



Bazas. Bordeaux. 



\ Limestone of Le Son. 

 3. Grey limestone of I Shell marl of Lariey. 



Agen. ^' { Freshwater limestone 



(^ near Saucats. 



Aquitanian. 2. Sandstone of Bazas. 2. Yellow sandy rock ex- 

 posed in valleys. 



I. White sandstone of i. Marl with A^m//«a/V;-z^- 

 Agen . sacci ( Nerita picla ) . 



* Contribution a I'etude de I'^tage tongrien dans le D^pt. de la Gironde, 

 Mem. Soc, des Sci. phys. et Nat. de Bordeaux, 1895, Tome V, p. 269. See 

 also Esquisse Geologique du Dept. de la Gironde, Feuillcs des jeuiies Nat- 

 uralisles, 1S89, and Esquisse d'une carte geologique des environs de Bor- 

 deaux, 1895. 



